pinctrl: pinctrl-adi: combine multiple groups of one function together

The data pins of some peripheral are different if connecting to different
devices in one pinmux function. In the PPI case, data pins can be used
in 8, 16 and 24 pin groups individually. Add these groups into one ppi
function.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>